1. Field of the Invention
The present invention generally relates to a method and apparatus for testing photovoltaic devices.
2. Description of the Related Art
In the production of photovoltaic devices, it is well known to use devices to reproduce a radiation that simulates the solar spectrum to carry out necessary tests and inspections on objects to verify operating reliability and overall conversion efficiency of photovoltaic devices under laboratory conditions.
The industry have developed standards that define solar simulator performance in three performance areas: spectral frequencies match to the solar spectrum, spatial uniformity of irradiance on the surface of the object to be illuminated, and temporal stability of light quantity produced. In the conventional solar simulators, xenon arc lamps have been widely used. However, xenon type lamps have some drawbacks. For example, the light produced by the xenon arc lamps contains fairly strong intensity peaks in the near infrared region that are not found in any of the standard solar spectra. Accordingly, xenon arc lamps suffer from poor homogeneity of output light distribution and irradiance efficiency, as well as poor spectral accuracy between the spectrum produced by such lamps and the solar spectrum.
Another drawback of xenon type lamps is that the output light spectrum is typically adjusted by varying the intensity of light by controlling the electric current and voltage supplied to the lamps. However, modifying these parameters generally affects all the wavelengths produced by the lamps. Therefore, it is not possible to select and modify individual wavelength so that the light spectrum produced by the lamps in different applications are as similar as possible to solar spectrum.
A further drawback of xenon type lamps is that irradiance intensity of the lamps is normally not stable but subjected to fluctuations due to variations in the current (supplied to different lamps) caused by a change in environment or power conditions. This influences the amount of fluctuations in the output spectrum produced by the lamps and therefore the reliability and repeatability of the results obtained from the tests.
Therefore, there is a need in the art to improve reproducibility and efficiency of the output spectrum produced by solar simulators under any given circumstances.